(1) Field of the Invention
This invention relates to the chemical analysis of substances, and more particularly, to apparatus for the automatic metering of biological fluids onto test slides.
(2) State of the Prior Art
In recent years, a number of automated systems have been developed for carrying out quantitative chemical analyses of fluid samples. Most of the commercially-available systems utilize liquid reagents and require analyzer equipment having intricate solution handling and transport capabilities. One widely used system, shown in U.S. Pat. No. 2,797,149, employs a continuous-flow technique in which successive samples are separated from one another by immiscible fluid segments such as gas or air bubbles. Such a system is complex and expensive, requires skilled operators, and necessitates a considerable expenditure of time and effort in repetitive cleaning operations.
As an alternative to liquid analysis systems, various essentially-dry analytical elements have been adopted for automated test procedures. Although these elements offer substantial storage and handling conveniences, compared to "wet-chemistry," they have enjoyed only limited success and have been used primarily for qualitative and semi-quantitative test purposes. Apparatus for use with integral analytical elements in the form of continuous webs is shown in U.S. Pat. Nos. 3,036,893, and 3,526,480. Since reagents are contained on the web in a predetermined sequence, the versatility of this apparatus is quite limited. Further, because of the peculiar properties of blood sera and the need to successively dispense samples from different sources, without contamination, such apparatus does not meet the requirements of this invention.
There is disclosed in the aforesaid commonly-owned application of R. Columbus, U.S. Ser. No. 644,014, a recent innovation in devices for metering biological fluids such as blood sera. This application discloses apparatus which dispenses through a cup-like container especially designed to repeatedly dispense precise micro-quantities of blood serum. Each container is used for only one serum sample so that, among other things, contamination problems are alleviated. However, there is no provision in the disclosed apparatus for the metering from substantially closed containers, and the containers must be moved into fluid communication with a stationary metering head.
The patent to G. F. Binnings et al., U.S. Pat. No. 3,574,064, discloses a fluid applicator in which a fluid container comprises a plurality of reservoirs from which a fluid is discharged onto laboratory slides. Each of the reservoirs contains a siphon tube having one end in the fluid and a second end in communication with a discharge orifice. Discharge of the fluid is accomplished by covering the top of the reservoir with a rubber cup which is compressed to produce a slight air pressure over the fluid in the reservoir; the air pressure causes fluid to be forced through the siphon tube and out the discharge orifice. Since the quantity of fluid discharged would vary, depending on the amount of air trapped by the rubber cup and on the degree of compression of the cup walls, this type of applicator would not be suitable for accurately metering extremely small amounts of fluid. The open reservoirs in the fluid container and the open rubber cup would present serious contamination problems.
The patent to Rochte et al., U.S. Pat. No. 3,540,586, discloses a vacuum head which is adapted to be brought into sealing engagement with a filter cup. With the head in the engaged position, a vacuum is applied through the head to lower the pressure within the filter cup, causing filtrate to be drawn into the cup through a porous bottom thereof. There is no suggestion in this patent as to the use of the disclosed apparatus for the precise metering of fluids.
U.S. Pat. No. 2,363,474, discloses a manually operated liquid dispenser having a cover for the metering tip. Such a dispenser, however, is not intended for use with an automatic chemical analyzer.